Today my kiddies, we begin covering the application of dimensions as described in Section 1.7 of ASME Y14.5M-1994. There is a lot of information to cover so I will break it up over 2 weeks. Like I said before ASME standards are easy to handle in small doses. So pinch your nose and hold your breath, here comes your weekly dose of ASME goodness.

Dimension Lines

Dimension lines show the direction and length of dimension with arrows at each end. Dimension lines should be broken to make room for the numerical dimension. If you do not place the dimension inside the dimension line then you can place it parallel to and above the dimension line. You must not use centerlines, extension lines, phantom lines, or object lines as dimension lines.

Alignment

Align dimensions and group adjacent dimensions to improve the look and readability of drawings.

Spacing

Dimension lines are to be drawn parallel to item being dimensioned with the first dimension spaced no less than .393″ (10mm) from the object. Each dimension after that is to have no less than .236″(6mm) spacing. Of course, the standards police are not going to write you a ticket if you don’t maintain this spacing. It is meant to meet the reproduction requirements for your industry. Besides, it just looks better.

Also, if you have many parallel dimensions you should stagger the numbers of the dimensions to make it easier to read. Dimensions all bunched up are not exactly easy to read, especially if you maintain good dimension spacing.

Crossing Dimension Lines

You should always try to avoid crossing dimension lines. Sometimes moving a dimension to another view will help but when you cannot avoid it do not break the dimension lines.

Extension Lines

Extension lines extend from the object after a short cap to just beyond the dimension line. Extension lines should be perpendicular to the dimension lines but can be shown at an oblique angle when space is limited like when two extension lines are too close to each other. Even when the extension lines are oblique the dimension lines are still parallel to the object being dimensioned.

Crossing Extension Lines

As with dimenison lines you should always avoid crossing extension lines. Dimensioning outside-in can reduce the chance of crossing extension lines. However, you will not always be able to avoid crossing, when this is the case do not break the crossing extension lines. If an extension line crosses an arrowhead or comes close to an arrow head, you can  break the extension line.

Location Points

Locating points, or virtual sharps as they are known in SolidWorks, should have extension lines extending from the object lines intersecting the point. This can be done using the witness or dot option for virtual sharps in the Document Properties.

That covers it for today. Come back next week for part two of the ‘exciting’ coverage of application of dimensions per ASME Y14.5.

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